1. Field of the Invention
This invention relates to a method for bringing under control, a well which is out of control, i.e., a well penetrating a subterranean formation wherein the formation pressure exceeds the pressure exerted by the hydrostatic head of fluid in the wellbore so that fluids flow from the well to the surface at an uncontrolled rate. Such fluid may be gases or liquids, and are usually combustible hydrocarbons, though they may also be water, brine, steam, emulsions, and the like. An uncontrolled well is sometimes described as a "blow out". More particularly, the invention relates to a method for bringing a first well under control wherein fluid is pumped down an adjacent second well, through the formation, and thence into the first well until the first well is brought under control.
2. Description of the Prior Art
Occasionally, formation pressure driving fluid out of a subterranean formation and into a wellbore penetrating such a subterranean formation becomes greater than the pressure exerted by the hydrostatic head of fluid in the wellbore, to the extent that a "blow out", or uncontrolled flow of fluid from the well, occurs. Sometimes the fluids may ignite accidentally, and in other instances may be deliberately ignited. For example, on land, it may be desirable from a pollution standpoint to permit an out of control well to burn until it can be brought under control, whereas on offshore wells, it may be desirable to extinguish the fire as soon as possible because of potential damage to the offshore platform. Various mechanical blow out preventers typically having hydraulically activated rams have been developed which frequently enable wells to be brought back under control by closing the blow out preventer until sufficient well-controlling fluids can be injected into the well. However, such techniques cannot always be utilized, for example, (1) where the pressure may exceed the capacity of the blow out preventers; (2) where blow out preventers may not close properly because of malfunction, improper installation, and the like; (3) where the blow out is at least partially occurring around the outside of the casing; (4) where the well head is so badly damaged that remedial connections cannot be made; etc.
Another technique that may be employed is to treat the well which is out of control through an adjacent well. If a nearby well is not available, an adjacent well is drilled. Ideally, the second well is drilled directionally so that it intersects the first. As a practical matter, however, the second well usually misses the first, and the well-controlling fluid is injected into the second well, through the formation, and then into the first well until the first well is brought under control.
The art of hydraulic fracturing of subterranean formations is well known.
Various techniques have been proposed for placing propping agents in fractures to prevent the fractures from completely closing, or "healing", when the wellhead pressure is relieved. Most involve the injection of multiple stages of fluids. Henry, U.S. Pat. No. 3,245,470 employed alternating foam stages to achieve deposition of proppant. Braunlich, Jr., U.S. Pat. No. 3,335,797 teaches a method for controlling the downward growth of fractures by a prop placement technique. Hanson et al., U.S. Pat. No. 3,151,678, teach to impart a surging action to the proppant as it is injected. Tinsley in U.S. Pat. Nos. 3,592,266 and 3,850,247 teaches methods whereby an effort is made to prop the fracture at intermittently spaced intervals.
Kiel, U.S. Pat. No. 3,933,205, and Winston, U.S. Pat. No. 3,948,325, teach methods of fracturing for creating multiple fractures, wherein the formation is permitted to heal at least partially between injection stages. In Kiel, the intermediate healing step is said to create spalling of the fracture faces. In Winston, the relaxation step following injection of what the patentee calls a "Bingham plastic fluid" is said to create a long plug against which a pressure can be applied to create a second fracture. In both Kiel and Winston, the high viscosity fluid may carry a proppant. Where Kiel employs a proppant, he teaches to follow the proppant stage with a viscous flush, e.g. Super Emulsifrac fluid having no proppant, prior to the healing step. See, for example, the treatment report in columns 21 and 22, Event Nos. 8-10. Winston teaches the Bingham plastic fluid may contain a propping agent (col. 4, line 22,) and may be followed by displacement fluid (col. 3, lines 32-34). In Example 1, Winston follows a borate gelled guar fluid containing proppant with a water stage prior to relieving pressure. In neither Kiel nor Winston, however, is it taught to follow the proppant stage with both a viscous, proppant free spacer and a non-viscous proppant free fluid, prior to the relaxation step.